Патент USA US3034005код для вставки
May 8, 1962 F. L. PUTZRATH 3,033,995 CIRCUIT FOR PRODUCING AN OUTPUT VOLTAGE INDICATIVE OF THE ABSOLUTE VALUE OF THE DIFFERENCE BETWEEN Two INPUT VOLTAGES Filed Aug. 51, 1960 4/ m r; % Zé 22' 4/0 (uRREA/T now THROU§II EITHER MUM/CW /:L___ 1 Err BRANCH curorg-l 2 R14”? BRA rVC/l (urapp, . '5 135. 6 O +5 * INVEN TOR. 142%’: L Parr/mm BY United States Patent G 1 ' 3,033,995 ' HNDECATIVE UP THE ABSQLUTE VALUE OF TEE DH‘FERENCE BETWEEN TWO INPUT VGLTAGES Franz Ludwig Putzrath, Oakiyn, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Aug. 31, 1960, Ser. No. 53,212 6 Claims. (Cl. 307-885) Patented May 8, IQGZ current flows from terminal 24, through resistor 28, through the ‘base-to-emitter diode of transistor 12, through resistor 18, through the emitter-to-base diode of transis tor 10, through resistor 34- to terminal 26. )Since emitter to-base current ?ows through transistors 10 and 12, col lector current also ?ows through these transistors and a given output voltage appears across output terminals 36. Current does not flow through transistors 14 and 16. The reason is that the polarity of the input voltages V1 and This application relates to a new and improved dif ' ICC 2 cmourr FQR PRODUCING AN OUTPUT VOLTAGE ference ampli?er. : > ‘In some pattern matching equipments such as used in communication systems, reading machines, shape recog 10 V2 is such ‘as to reverse bias the emitter-to-base diodes of transistors 14 and 16. —4 volts is applied to the base of transistor 16 and —2 volts is applied to the base of tran sistor 14 and the voltage diiference is therefore in a sense to reverse bias the emitter-to-base diodes of both tran nition machines, and the like, it is necessary to compare 15 sistors. two input quantities such as voltages or currents and to Assume now that the input voltage V1 is -—4 volts and derive therefrom an output signal which is proportional to the input voltage V2 is —2 volts. The di?erence in volt the difference in these quantities. In certain of the above age between V1 and V2 is now of polarity to forward applications it is desirable to determine only the absolute bias the emitter-to-base diodes of transistors 14- and 16 magnitude of the di?erence in quantities regardless of 20 and to reverse bias the emitter-to-base diodes of transis which of the quantities is larger, and regardless of the tors 10 and 12. Current now ?ows through transistors 14 absolute value of either of the quantities. Conventional and 16 and transistors 10 and 12 are cut on‘. The output di?erence ampli?ers do not meet these requirements as voltage across terminals 36 is exactly the same ‘as the out they produce an output having a sense dependent upon put voltage at these terminals when V2 is —4 volts and which of the input quantities is the larger. . 25 V1 is —2 volts. . The circuit of the present invention solves the problem If the voltage V2 should change to a value of -—6 volts above in a simple, reliable and relatively inexpensive way. and the voltage V1 to a value of -—4 volts, the absolute The circuit includes two parallel si@al paths, each com magnitude of the difference in voltage'is still 2 volts. prising two transistors of opposite conductivity connected Under these conditions, the same amount of current flows in series. An operating voltage is applied to the transis 30 through the emitter-to-base diode of transistors 10 and tors in both paths through a common load impedance. 12 as when the voltages V2 and V1 are —4 ‘and —2 An input voltage having a magnitude equal to the dif ference between two input quantities is applied in one volts, respectively. Accordingly, the voltage V3 at tenni nals 36 is again the same as in the cases described above. sense between the bases of the transistors in one path and When V1 is equal to V2, there is no difference in voltage» in an opposite sense between the bases of the transistors 35 applied between the bases of any of the transistors. For in the other path. An output voltage which is propor example, the same voltage is applied to the base of tran tional to the di?erence ‘between the two input quantities sistor 14; as to the ‘base of transistor 16. Accordingly, no appears at the common load impedance. The sign of current ?ows in the emitter-to-base diodes of these tran the output voltage is independent of the sense of the dif sistors, and since no base current ?ows, no collector cur ference between the input quantities or the absolute value of either of the input quantities. The invention is discussed in greater detail below and is illustrated in the following drawings of which: FIG. 1 is a schematic circuit diagram of the present invention; and FIGS. 2 and 3 are graphs illustrating the performance of the circuit of FIG. 1. rent ?ows. Accordingly, the output voltage V3 at termi nals 36 is ~25 volts. The same analysis holds for tran sistors 10 and 12. -No emitter-to-base current ?ows in either of these transistors and the output voltage remains at —25 volts as already stated. The purpose of resistors 18 and 21) is to provide a small amount of reverse bias on the transistors. This ensures that there is essentially no current ?owing through the load resistor 22 when the two input voltages ‘are identical. An additional advantage due to resistors 18 [and 20 is that they provide a large amount of feedback. It is therefore The diiference ampli?er of FIG. 1 includes two parallel signal paths, the ?rst including two transistors 10 and 12 of opposite conductivity type connected in series and the other including two transistors 14 and 16, ‘also of opposite not necessary to balance transistors, and any units in a conductivity type, connected in series. Each of the signal production run may be used. . paths includes, in addition to the transistors, resistors 18 A practical circuit according to FIG. 1 may have the and 20, respectively. An operating voltage, shown as —25 following values of circuit elements: volts, is ‘applied to the transistors through a common load 55 Resistor-s 28, 30, 32 and 34—10,000 ohms each impedance, such as a resistor 22. Resistors 18 and 20~2,700 ohms each The two input voltages V1 and V2 are concurrently ap Resistor 22—5,600 ohms plied between terminals 24 and 26, respectively. One of PNP transistors 10 and 14-—2 N 404 terminals 24 is connected through resistors 28 and 30' to the bases of the NPN transistor 12 in one path and the 60 NPN transistors 12 and 16-2 N 440 PNP transistor 14 in the other path, respectively. One A circuit with the values of components above and the of terminals 26 is similarly connected through resistors 32 and 34 to the bases of the NPN transistor 16 and PNP transistor 10, respectively. The other of the termi operating voltage shown produces outputs as shown in .FIG. 2. It may be seen that the same output voltage is produced for a given difference in input voltages, regard nals 24 and 26 are connected to a point of reference po 65 less of the magnitudes of the input voltages or the sense tential, shown as ground. of the difference. This is also shown in a somewhat dif The operation of the circuit of FIG. 1 may be better ferent way in FIG. 3 which illustrates that the output understood by assuming certain input voltages. Assume voltage depends only on the difference in magnitudes of ?rst that voltage V2 is somewhat more negative than the input voltages and not on the individual magnitudes of voltage V1. For example, voltage V2 may be -4 volts and voltage V1, —2 volts. Under these conditions, the 70 the input voltages or the sense in the difference in the sense of the voltage difference is such that “conventional” magnitudes. - - : 3,033,996 ,. y r .What is claimed is: ,1 a 3 4 . ' ' one conductivity type in one circuit and the base of a ' transistor of opposite conductivity type in the other cir 1. iin combination, two circuits connected in paralle , cuit; and means for applying a second input signal to the bases of the other two transistors. ‘ ,l connected in series; a common load impedance connected 5. A difference ampli?er comprising, in combination, _ in series with the two circuits through which an operating Cl a ?rst pair of transistors of opposite conductivity type voltage for all of said transistors may be applied; means , connected in series ,emitter-to-emitter; a second pair of .t'or applying .‘an input voltage across the bases of the each comprising two transistors of opposite conductivity transistorsin one circuit; and means'ior applying the ' same inputjvoltage in an opposite sense across'the bases of the transistors in the other circuit. ‘ a, 10 - 2. In combination, a ?rst pair of transistors of opposite conductivity type connected in series and in a sense to conduct current in the same direction; ‘a second pair of transistors of opposite conductivity type connected in series and in a sense to conduct current in the same di transistors of opposite conductivity type connected in series emitter-to-emitter; a ?rstvcommon connection at the collectors of two of'the transistors of like conductivity type; a second common connection at the collectors of the other two transistors; a load impedance connected at one terminal torsaid ?rst common connection for supply ing an operating voltage’ to the transistorsg‘means for applying ‘a first input signalbetween said second common rection, the two pairs of transistors being connected in connection and the bases of :two transistors, one in each parallel; a load resistor connected to both pairs of tran pair, of opposite conductivity type; and means for apply sis'tors through which an operating voltage for all of said transistors may be applied; and means for supplying a diiference voltage across the bases ‘of one pair of tran: sistors ‘and for supplying the same voltage in opposite polarity across the bases of the other pair of transistors“ 3. ‘In combination, two circuits connected in parallel, ing a second input signal between said second common connection and the bases of the other two transistors, one each comprising two transistors of opposite conductivity similarly connected in series, like electrode to like elec trode; acommon load resistor connected in series with the two parallel circuits for applying an operating volt pair of opposite conductivity'type; 270 in 6.,each A di?ference ampli?er comprising, in combination, a ?rst pair of transistors of opposite ‘conductivity type connected in series emit-ter-to-emitter; a second pair of ‘transistors of opposite conductivity type connected in series emitter~to~emitter; two resistors of like value, each connected in seriespwith a pair of transistors between ' emitters; a ?rst common connection at ‘the collectors of two of the transistors of like conductivity type; a second age to said transistors; and means for applying an input I voltage in one sense between the basesof the transistors " common connection at the collectors of the other two in one circuit‘and'in an opposite sense between, the bases so transistors; a load impedance connected at one terminal of the transistorsin the other circuit. 7 ' ' ‘to said ?rst common connection for supplying anoperat 4. 'In combination,_rtwo parallel circuits, each compris- ing voltage to the transistors‘, means for applying a ?rst series emitter-to—emi-tter; a two, terminal common load ' the bases of two transistors, one in each pair, of opposite conductivity type; and means for applying a second input signal between said‘ second common connection and the ,ing two transistors of opposite conductivity connected in ' 1 input signal between said second common connection and resistor for ‘the two circuits connected at one terminal to the collectors of the two transistors of one conductivity type, whereby an ‘operating voltage may be applied be bases of the other two transistors, one in each pair, of tween the other terminal of said resistor and the collectors > opposite conductivity type. of the transistors'of other conductivity‘ type; means for applying one input signal to the base of a transistor of 40 ,No references cited.